In the conventional vehicle engine, as shown in FIG. 1, the crankshaft 2 passes through the front engine cover 3 to provide motive power to the front end accessory drive (abbreviated as FEAD, not shown in the figure) installed at the outside of the front cover 3. When the crankshaft 2 passes through the shaft bore 4 on the front cover 3, the axle seal 1 is needed to provide the engine with sealing protection for preventing the lubricating oil from leaking to the outside from the engine.
In the conventional engine, the front cover 3 is generally made of steel or aluminum stamped plate; both the position and the dimensions of the shaft bore 4 are relatively accurate, so when the crankshaft 2 passes through the shaft bore 4, sealing can be implemented with the use of conventional oil seal. There are two common types of conventional oil seals: one type is the radial lip shaft seal, which uses fluorine rubber material to be in sealed contact with the crankshaft surface through a spring-restrained rubber lip; the other type is the polytetrafluoroethylene (PTFE) seal, which uses the seal lip with a flex section to be in sealed contact with the crankshaft surface through flexural fitting. Regardless of which type it is, it can only tolerate within a certain range the shaft-to-bore misalignment (generally referred to as “static misalignment”) between the rotating shaft and the shaft bore as well as the dynamic runout (also referred to as “dynamic misalignment”) when the rotating shaft rotates.
With the development of technology, front cover producers hope that plastic material can be used to replace the conventional steel or aluminum material, so as to achieve the objective of reducing noise, lowering weight and reducing cost. However, the replacement of material also brings a challenge to the shaft bore sealing between the crankshaft and the front cover. This is because, in comparison with the metal material, the dimensional tolerance of the front cover made of plastic material is larger; it is more difficult to control the bore position and dimensions thereof in comparison with the metal material, so that it is easy to make the shaft-to-bore misalignment reach or even exceed 1 mm when the crankshaft passes through the front cover. After the temperature rises, the heat distortion of the front cover may also further aggravate such misalignment. When the shaft-to-bore misalignment exceeds a certain range, it will be difficult for the lip of the conventional oil seal to be in full contact with the crankshaft surface, which results in damage to the normal sealing status. The present invention comes into being due to the challenge of this type of new front cover.